This invention relates to knife sharpeners of the kind which sharpen a knife blade as a result of the cutting edge of that blade being moved over the sharpener. It will be convenient to hereinafter describe the invention in relation to such sharpeners as used in combination with a scabbard or other protective cover for the blade.
U.S. Pat. Nos. 3,676,961 (Jackson), 3,774,350 (Bayly), 4,041,651 (Bayly) and 4,091,691 (Bayly) relate to scabbard-sharpener conbinations as referred to above. Those prior constructions have been satisfactory for sharpening standard blades, but they are not entirely suitable for use with special blades having a narrow tip. Narrow tip blades are used for delicate cutting operations such as filleting fish, and it is important that the cutting edge of such blades be kept in good condition right up to the very tip of the blade. Prior blade sharpener combinations as referred to above are unable to satisfy that requirement.
The Jackson blade sharpener includes means for maintaining downward pressure on a knife blade during its passage across the actual sharpening device. That pressure applying means is so arranged, however, that it does not engage the knife blade until that blade is moved inwardly some distance beyond the sharpening device and loses contact with the blade during withdrawal before the blade has left contact with the sharpening device. It follows that the cutting edge at the tip portion of the blade is not subjected to the same sharpening control as are other parts of the blade and is therefore not sharpened properly.
The Bayly blade sharpeners are arranged so that pressure applying means of one form or another engages and bears down on the back edge of a blade close to the time at which the blade cutting edge first contacts the sharpening device. In spite of that early contact, the sharpeners have a configuration such that they are unable to effectively sharpen the tip portion of a narrow blade. Each of those sharpeners is arranged to operate with knife blades of substantial depth, even close to the tip, and the maximum downward force on the blade is achieved while the deeper sections of the blade are moving over the sharpening device. Minumum downward force and consequently minimum sharpening effect is achieved while the tip portion of the blade is moving over the sharpening device.
It is an object of the present invention to provide a blade sharpener which is able to effectively sharpen a blade up to the very tip thereof. It is a further object of the invention to provide a blade sharpener which is particularly suited for use with blades which are relatively narrow or have a shallow depth.